Primate community structure at twenty western Amazonian flooded and unflooded forests

This paper presents data from a standardized series of line-transect censuses on the species and subspecies composition, population density, and crude biomass of western Amazonian primate communities occurring at eight flooded (=varzea) and 12 unflooded (=terra firme) forests. These were located primarily along one of the largest white-water tributaries of the Amazon (=Solimoes), the Jurua river. On average, terra firme forests contained twice as many primate species, lower population densities, and less than half of the total community biomass than did adjacent varzea forests. There was a clear habitat-dependent positive association among primate species, particularly within varzea forests, as well as marked shifts in guild structure between forest types. Species turnover between these two forest types involved primarily understorey insectivores (e.g. Saguinus sp.), which do not occur in seasonally inundated forest. These were consistently replaced by squirrel monkeys (Saimiri sp.), which are extremely abundant in annually flooded varzea forests. Similarly, large-bodied folivores such as red howler monkeys (Alouatta seniculus) were uncommon or rare in terra firme forests, but very abundant in varzea forests, even though they are hunted less intensively in the former than in the latter. This can be largely explained by the nutrient-rich alluvial soils of young floodplains, compared to the heavily weathered terra firme soils occurring even within short distances of major white-water rivers. This study clearly shows a reversed diversity/density pattern resulting from the lower species richness, but high overall community biomass of seasonally flooded Amazonian forests, which can now be generalized for a wide range of terrestrial vertebrate taxa, including amphibians, birds, and several other orders of mammals.